Let’s rebuild an 18v Ryobi/Worx/Skil battery pack

Let’s rebuild an 18v Ryobi/Worx/Skil battery pack

I love my Ryobi impact driver, but since day one the battery packs have given nothing but trouble. The Ryobi ONE Ni-Cad packs will leak down rapidly after a full charge. A full battery pack will be dead in just a day when sitting on the work bench. At first I thought there was a parasitic draw in the impact driver itself, but that wasn’t case. Just leaving a pack sit idle for a day was enough to drain it. This meant that the battery packs would have to sit constantly in the charger to be ready for work — that’s not a good idea because it really shortens the life of the pack.

After two years the batteries were shot — wouldn’t hold a charge for more than 5 minutes. New packs are about $40, but then I’d be back in the same rut. So I decided to upgrade the packs with better batteries.

The OEM batteries are really cheap 1200 mAh sub-C cells. I decided to upgrade to 2500 mAh sub-C cells. Found an eBay deal for 16 cells for $14 INCL. shipping.

Sorry for the poor pics but I used my phone camera on this project. I forgot my good camera at the office. This is the pack in question

The pack is held together by some Phillips screws and is easily taken apart.

The first thing I noticed is a Thermistor that is taped to the left battery. The Thermistor is supposed to shut down the charging process in case the battery pack overheats to a very high degree due to damage or a short. This is a good thing because these packs do get abused in the field, but I think that it’s the Thermistor that causes the battery pack to slowly discharge within a day or so. This is a design problem — ?

Batteries are glued to an indexing card

Make note of how everything hooks up and gently start taking things apart.

All 15 1.2volt batteries in the case are simply hooked up in series (15x 1.2 = 18volts)

Save the index card as a template for arranging the new batteries.

The only pieces that need to be saved from the old battery connections are the connecting tabs for the Thermistor and the  step down tab for the last battery in series. The last battery in series is mounted on top of the battery pack and resides in the connection stem of the pack.

The new batteries come with cheap tabs on top which can’t be repositioned to configure a battery pack structure that will fit in the battery case. So I cut the old tabs and sent away for nickel strips that can be readily soldered in any position required.

I used the indexing card to align the batteries in series and then used tape to hold them in place for soldering. First the top joints, then the bottom. I just followed the original solder patterns on the old batteries.

When everything was soldered up and positioned in place, I took a voltage reading and it showed 19.3v — this surface charge normal for newly charged batteries. These new batteries come shipped fully charged, so I was careful to avoid accidental shorts when soldering.

Everything is buttoned back up and stuffed back in the case

The pack is inserted back in the tool and everything works. It definitely has more power — let’s hope it discharges a lot slower. The Thermistor will still leak, but I’m hoping the extra power will make the leakage less noticeable.

Took about 1.5 hours to do this job. We’ll see whether it was worth it. — LOL

NOTE: I had a few personal messages about battery sizing. Batteries are rated in milli-Ampere hours (mAh)– which is the capacity of the  battery to discharge while under load. A higher mAh rating means the battery will last longer under load. That said, you shouldn’t assume that substituting the highest mAh battery in a rebuild is OK. Higher mAh ratings also effect your charging rate and charging temperatures, and depending on the quality of your charger it may put too much load on the unit. That could cause a melt down or a short in the charger or the battery pack — remember the Thermistor in the battery pack? If the heat gets too high, the Thermistor will shut it down and you may need a new Thermistor and/or a new charger.

Bottom line – it’s best not to exceed double the mAh rating of the original battery packs. In my case it was 1200 mAh and I opted for 2500 mAh. Higher capacities are out there, but why risk it.

 

 

Source: http://www.thegaragegazette.com/index.php?topic=16306.0